Videolights

Jim Church's Cows
Part III

by Roger Roth

PART V -- RELATIONSHIPS BETWEEN APERTURES, SHUTTER SPEEDS AND FILM SPEEDS
GIVE US "THE GRAND TRADE-OFF."

QUICKIE REVIEW

Each higher-numbered full f-stop (such as going from f8 to f11) admits
half as much light at any given shutter speed. Each lower-numbered full
f-stop (such as from f11 back to f8) admits twice as much light. (I
said "full" because there are some in-between stops, such as
f4.5 or f9.)

Each higher-numbered consecutive shutter speed admits half as much
light (such as going from 1/30 to 1/60). Each lower-numbered shutter
speed (going back from 1/60 to 1/30) doubles the amount of light admitted.

Each higher-numbered (doubled) ISO rating means that the film needs
half as much light for an exposure (ISO 200 needs half as much light
as ISO 100). Each lower-numbered (halved) ISO rating requires twice
as much light (as from 200 back to 100).

BIG THOUGHTS ABOUT RELATIONSHIPS

Notice how are most changes are either "double or half? (Yeah, going
from 60 to 125 fudges it a little and going from ISO 64 to 100 is still
within one-third of an f-stop. But what the heck, you got the idea;)

Each change in f-stop, shutter speed or ISO either admits or requires
either twice as much or half as much light.

The changes in apertures, shutter speeds and film speeds are related
because the changes are "equal." This leads us to The Grand
Trade-off.

THE GRAND TRADE-OFF: BOVINE EXPLANATION

To help visualize THE GRAND TRADE-OFF, think about The Grand Trade-off
from Elmer's point of view:
On any given afternoon, Elmer can nap, graze or socialize with Elsie.
Given that he has only so much daylight and time during the afternoon,

Elmer must make some choices:

If Elmer chooses to nap, he must give up some grazing and socializing
time. (Calves love this because they can play "king of the
mountain" on his rotund belly.)

If Elmer chooses to graze, he must give up some napping and socializing
time. (Elsie loves this because it keeps Elmer occupied.)

If Elmer chooses to socialize, he ends up tired and hungry. (And
so does Elsie.)

(There are outside factors that influence Elmer's choice of activities--such
as: how many hours of light does he have, how good is the grass and how
fast can Elsie run. Sorry, Elmer. Nobody said making decisions was easy.)

REAL-LIFE LOOK AT THE GRAND TRADE-OFF

There are three areas in which you may strive to gain an advantage:

You may want low film speeds for fine grain and good color.

You may want small apertures (high f-numbers) for more depth of field.

You may want fast shutter speeds to stop the action.

Any choice you make has a price which you will pay in one or more of
the other areas: For example, a slower ISO film speed will force you
to use a wider aperture, slower shutter speed or both.

To summarize:

A slow film speed gives you fine grain and color, but you lose either
depth of field, the ability to stop action or both.

Small apertures give you better depth of field, but at the cost of
increased grain, the ability to stop fast action or both.

Fast shutter speeds let you stop the action, but at the cost of more
grain, less depth of field or both.

There are outside factors that influence your decision, such as how much
light do you have--sun or strobe--how fast are your subjects moving,
and do you have both near and far subjects. As Elmer would say, "Sorry,
Charlie; there ain't no such thing as a free bail of hay, or a roll in
it.")

HOW TO REMEMBER THE GRAND TRADE-OFF

Compare yourself with Elmer. Elmer's choices were napping, grazing or
socializing--all easy to remember. Your choices are: fine grain, stop
the action or depth of field--also easy to remember. Your choice depends
on how you wish to utilize the light you have to take the exposure. (Just
think "GAD."

PART VI -- WIDE-ANGLE AND TELEPHOTO LENSES

The designations "wide-angle" and "telephoto" are
determined by focal length. Lenses with short focal lengths, such as
a 15mm lens for a 35mmcamera, are wide-angle lenses. Lenses with long
focal lengths, such as a 100mm lens for a 35mm camera, are telephoto
lenses.

BOVINE EXPLANATION

Imagine that Elsie has her rump pressed firmly against the back fence,
and that she is looking out through the gate. If the distance from the
fence to the gate is short, Elsie's view through the gate (of the other
field) is quite broad. If the distance from the fence to the gate is
long, Elsie's view of the other field is quite narrow. Thus, a short
fence-to-gate distance gives her a wide view; a long fence-to-gate
distance gives her a narrow view.

REAL WORLD EXPLANATION

Think of the back fence as the film.

Think of the gate as the aperture.

Think of the fence-to-gate distance as the focal length.

Think of "angle of view" as the width of the view Elsie
sees through the gate.

The shorter the focal length, the wider the angle of view the lenses.
The longer the focal length, the narrower the angle of view the
lens sees. A 15mm lens sees a wide angle of view, a 100mm lens sees a
narrow, telephoto angle of view.

How can you remember this stuff: easy--just think of Elsie backed up
against the fence and looking through the gate, and then imagine some
different Elsie-to-gate distances.

QUESTION: Wouldn't the width of the gate opening also affect the width
of the view?

ANSWER: While changes in the width of the aperture
might make itsy-bitsy changes in the angle of view a lens sees, the
curvature of the lens elements negates this problem.

JACOBY EYEBALL ANTICS

Dick Jacoby uses a different example to illustrate wide-angle and telephoto
lenses. To paraphrase Dick:

Make a large circle with your thumb and first finger tip. PRETEND
THE OPENING IS THE APERTURE OF A LENS.

Hold your hand in front of one eye and look through the opening.
PRETEND THAT YOUR EYE IS THE FILM.

PRETEND THAT YOUR EYE-TO HAND DISTANCE IS THE FOCAL LENGTH.

If you hold your hand close to your eye (a short focal length) you
will see a wider view than if you hold your hand farther from your eye
(a longer focal length).

WHAT IS A "NORMAL" LENS

A "normal lens" is somewhere between wide-angle and telephoto
lenses. Topside, a 50mm lens for a 35mm camera is considered "normal" because
it approximates the view of the human eye. Underwater (where a 35mm
lens acts like a 47mm lens) let's say that the 35mm lens is a "normal" lens
for underwater photography. Close enough for bovine work.

DEPTH OF FIELD AGAIN

Reminder: At any given focused distance and aperture--the wider the angle
of the lens--the greater the depth of field. Why? Because Elmer says
so. (Actually, the explanation is beyond the scope of my simplistic approach.)

Critter corner: Many cowfish are considered poor swimmers,
usually seen hovering more than swimming. During mating, many male cowfish
species will turn a different color and produce an audible hum.

Roger Roth is a roofer by trade and lives in Cincinnati,
Ohio. But his passion is underwater videography and after several decades
of learning how to shoot and edit he has evolved into a teacher and a
photographic philanthropist. Roger is the founder of the annual international Underwater
Images Photo and Video Competition. You may contact Roger at rroth2@cinci.rr.com.